So, using relativity, imagine the two Zodiacal settings superimposed on one another: Four of the tropical Signs are located by holding the four seasonal points, the Equinoxes and Solstices, in place. The other 8 tropical Sign-boundaries are measured from there.
Whereas, the sidereal Signs are located by using a particular star to locate one Sign, and the other 11 sidereal Signs are located from there.
Now, add in "Precession", which means that the Seasonal-points and the stars are moving, relative to each other.
The result is:
When the Seasonal-points are held in place, so is the tropical Zodiac. And, that means the sidereal Zodiac, affixed to a star, is rotating through the tropical Zodiac, with Direct-motion.
In contrast:
When the stars are held in place, so is the sidereal Zodiac. And THAT means, the tropical Zodiac, affixed to the Seasonal-points, is rotating through the sidereal Zodiac, with Retrograde-motion.